I want to add invoice numbering to a form.
The numering should be like this: RLZ-202410001
The next one RLZ-202410002 and so on.

I have read that this is done by a hidden field and script.

Can anyone help me with this issue.

Thanks.

I would be interested in that too. Have you made any progress here?
It's been a while.

If you had to find out how to get the last ID in the submissions, that would be the first step.

There is a placeholder: {last_insert_id}
But this probably only relates to the mapping. Doesn't anyone have a solution? If you use the payment plugins offered, it must be possible somehow.

I solved it for myself like this:

// Assumption: the table prefix is jos_ (replace it with your actual prefix)

$db = JFactory::getDbo();
$query = $db->getQuery(true);

$query->select('MAX(SubmissionId) AS last_submission_id');
$query->from($db->quoteName('jos_rsform_submissions'));

$db->setQuery($query);
$lastSubmissionId = $db->loadResult();

// Increase the $lastSubmissionId by 1
$lastSubmissionId++;

$aktuellesJahr = date("Y");
// Add zeros in front of the submission ID to get a 5-digit number
$fuenfstelligeID = str_pad($lastSubmissionId, 5, '0', STR_PAD_LEFT);

// Fill in your field "invoice number"
$val = "RG-" . $aktuellesJahr . $fuenfstelligeID;